Observation of movements inside and/or made by a patient, (e.g., in an examination region), is important or at least useful in many fields of medical examinations and/or interventions. In this regard, different variants have been proposed in particular in respect of imaging, which are based partially on auxiliary devices external to the image recording device, (e.g., respiratory belts, optical monitoring systems and the like), but sometimes also use capabilities of the image recording device itself. It has therefore been proposed, for example, in relation to magnetic resonance imaging, to use what are known as navigators, (e.g., simple, short magnetic resonance sequences to make observations about, for example, the movement of a specific edge, such as the movement of the diaphragm in respect of breathing), and to draw conclusions therefrom about the respiratory movement.
It is with magnetic resonance imaging that movement information proves to be useful for reducing artifacts. If, for example, gradients for spatial encoding are used for recording magnetic resonance data, the recorded magnetic resonance signals are susceptible to movement, and this applies to pure imaging as well as spatially resolved spectroscopic imaging. Movements cannot be completely avoided even with a stationary patient since the breathing as well as the cardiac movement are basically present, e.g., periodic movement patterns that may be taken into account. Existing movement information with respect to a partial movement of this kind may therefore be used, for example, to trigger data recording with a magnetic resonance device.
To ascertain movement information in examination regions, in particular, during magnetic resonance imaging, a novel process has been proposed in DE 10 2015 203 385.6, which is based on the use of an optionally additional excitation signal.
Specifically, it is proposed therein to generate an item of movement information relating to an at least partially moved examination region by outputting, (e.g., emitting), a first excitation signal having a first frequency band, which is then recorded with a receiving coil arrangement, (e.g., with a receiving coil arrangement of a magnetic resonance device), whose receiving frequency band includes the first frequency band. An item of movement information of the examination region may be ascertained from the recorded first excitation signal. This is based on the idea that differences result in the case of receiving signals from movements of the examination object, produced owing to the first excitation signal, which cause a change in the transmission properties of the signal path between the transmitter of the first excitation signal and the receiving coil arrangement. For example, the movement may cause a change in the quality of the coils of the receiving coil arrangement. It may also change the orientation of the receiving coil arrangement. Even when the first excitation signal potentially travels through the examination object, differences may result in the signal path as a function of the movement (change in the signal propagation in the medium). According to the subsequently published application, conclusions are to be made from these differences about the breathing or movement phase. The movement information may be used for movement correction of a scanning signal.
While the process may be carried out without a magnetic resonance device, since the first excitation signal is not a resonance signal, it is nevertheless advantageous to implement the process therein in a magnetic resonance device since there is a receiving coil arrangement present therein anyway. The first frequency band and a third frequency band required for receiving magnetic resonance signals may be located such that both are incorporated by the receiving frequency band of the receiving coil arrangement and, in particular, do not overlap. Therefore, the first frequency band does not collide with the high-frequency signal of the magnetic resonance device, which lies in a second frequency band, and the actual scanning signal, the magnetic resonance signal, which lies in the third frequency band. According to the subsequently published document, the movement information may be ascertained from a signal intensity, (e.g., at least an amplitude), of the receiving signal received on the basis of first excitation signal. In particular, in respect of ascertaining movement information relating to specific partial movements of the overall movement, (for example, respiratory movement or cardiac movement), it may, however, be maintained that all movements of the patient (and, depending on the position of the transmitter, also further movements) are contained in the receiving signals produced on the basis of the first excitation signals, and this may make evaluation difficult.